This invention relates to an automatic vending machine for vending cooled or refrigerated commodities such as a canned beverage, a bottled beverage in a glass bottle or a PET (polyethylene terephthalate) bottle, and various food items.
Generally, an automatic vending machine of the type comprises a heat-insulating commodity storage arranged in a main body of the automatic vending machine. The commodity storage has a commodity receiving column disposed therein to receive a number of items to be sold. When a particular item is selected by a customer, the particular item is delivered or discharged to a commodity outlet. The automatic vending machine further comprises a refrigerating circuit having a cooling unit disposed in the commodity storage, and a fan for circulating internal air within the commodity storage. By circulating the internal air through the cooling unit, the items in the commodity storage are cooled.
In order to prevent frosting or to perform defrosting, the automatic vending machine carries out a defrosting operation in which a cooling operation by the cooling unit is interrupted and the fan is continuously operated. The defrosting operation may automatically be carried out for a preselected time period at a predetermined time interval. In this case, every defrosting operation is performed for the preselected time period which is fixed irrespective of a frosting condition, i.e., the amount of frost. If the amount of frost is great, the preselected time period is too short to perform sufficient defrosting. On the other hand, if the amount of frost is small, the defrosting operation is excessively carried out to decrease a cooling efficiency in the commodity storage. Thus, it is difficult to efficiently perform the defrosting operation adapted to the frosting condition.
It is therefore an object of this invention to provide an automatic vending machine which is for vending cooled or refrigerated commodities and is capable of carrying out a defrosting operation adapted to a frosting condition of a cooling unit.
Other objects of the present invention will become clear as the description proceeds.
According to the present invention, there is provided an automatic vending machine which comprises a commodity storage for storing a number of items to be sold, a refrigerating circuit having a cooling unit connected to the commodity storage for cooling the items, a defrosting unit connected to the cooling unit for intermittently carrying out a defrosting operation for the cooling unit, a temperature sensor connected to the commodity storage for detecting a storage temperature within the commodity storage to produce a temperature signal, a calculating unit connected to the temperature sensor and responsive to the temperature signal for calculating a temperature variation rate prior to the defrosting operation, and a defrost control part connected to the calculating unit and the defrosting unit for controlling the defrosting operation with reference to the temperature variation rate.